1. Field of the Invention
The present invention concerns color management systems, and specifically concerns construction of colorimetric measurements from spectral measurements of the device, so as to assure interoperability with color management systems that rely on spectral measurements well as those that rely on colorimetric measurements.
2. Description of the Related Art
Color management systems historically found their roots in transform-based systems, in which a sequence of simple transformations was applied in order to convert from one color space to another. As an example, simple matrix multiplications might have been used. The coefficients in the matrices were stored in device profiles, which herein are designated as “transform-based” device profiles. Color management systems which used transform-based device profiles are herein designated as “transform-based” color management systems.
Over time, inadequacies were noticed in transform-based color management systems and their transform-based device profile counterparts. It was found that better performance could be obtained by creating device profiles that stored actual colorimetric measurements of the device's color characteristics. Such device profiles are herein designated as “measurement-based” device profiles, and the color management systems that used colorimetric measurements are herein designated as “measurement-based” color management systems.
The measurement information in a measurement-based device profile is colorimetric data, typically, CIEXYZ measurements. Measurement-based color management systems access the measurement data via a device model object. During the initialization process, the color management system accesses the device model object to obtain device colorant combinations and the associated measurements in order to build an analytical model of the device behavior for the specific condition indicated by the measurements in the device model profile. In addition to the device model information, a separate viewing condition profile is provided which contains measurements of the viewing environment under which a document is to be viewed. These measurements include a white point.
For purposes of backward compatibility, the inventor herein has previously worked to develop a conversion process, whereby measurement-based device profiles could be used in older transform-based color management systems. WO 2005/109318 is a recent publication of this work, and describes a process by which measurement-based device profiles are used to generate a corresponding transform-based device profile, which then could be used in older transform-based color management systems.
More recently, in connection with advances in color management systems, there is a desire to make use of spectral measurements rather than colorimetric measurements. The advantage of spectral measurements is that the appearance of colors can be determined under many different lighting conditions, thereby providing a more flexible tool for color management. In this model, the device profile will contain spectral measurements rather than colorimetric measurements, and the color management system will receive the spectral measurements from the device model object in spectral form. Spectrally-based color management systems, together with spectrally-based device profiles, hold out promise of unparalleled accuracy in color reproduction and fidelity.
For backwards compatibility purposes, however, a spectrally-based device profile cannot be used in current measurement-based color management systems.